Mode A code shortages
Thread Starter
Mode A code shortages
According to a 2001 Eurocontrol study, the effects of Mode A code shortage, which is the cornerstone of the case for Mode S equipage, should be kicking in and causing delays round about now, particularly in the London FIR. So, two sets of questions:
1) Is it currently possible to avoid allocating a Mode A code to an aircraft with a Mode S transponder? Is this the current practice? If not, when will we reach the point at which equipage with a Mode S transponder will "save" a Mode A code.
2) What evidence is there that we are at or approaching the capacity of Mode A codes in the London FIR (or elsewhere)? Are flights currently delayed through shortage of codes to allocate? If not, is there a way of finding out how close to capacity we are?
Thanks
1) Is it currently possible to avoid allocating a Mode A code to an aircraft with a Mode S transponder? Is this the current practice? If not, when will we reach the point at which equipage with a Mode S transponder will "save" a Mode A code.
2) What evidence is there that we are at or approaching the capacity of Mode A codes in the London FIR (or elsewhere)? Are flights currently delayed through shortage of codes to allocate? If not, is there a way of finding out how close to capacity we are?
Thanks
Beady Eye
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bookworm
In the UK mode 'S' is only under trial at specified locations. So it is not possible not to allocate a mode A.
Although there are currently no delays in UK it is only because codes are re-used quite quickly. This does occasionally trip the NAS computer up and aircraft are occassionally issued the same code, although not for long usually. Something that is being worked on. I would not like to speculate as to how close to capacity we are but given the general downturn in traffic not ver very, just quite
Although there are currently no delays in UK it is only because codes are re-used quite quickly. This does occasionally trip the NAS computer up and aircraft are occassionally issued the same code, although not for long usually. Something that is being worked on. I would not like to speculate as to how close to capacity we are but given the general downturn in traffic not ver very, just quite
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Bookworm,
In the US we run out of transponder codes almost weekly so we see proposed flight plans being assigned generic codes of 3100, 5400, etc. Since most approach controls have code subsets assigned to their facilities we can assign one of our local codes to any flight plan that has a generic code.
As for Mode S some facilities have the Mode S antennas and most don't.
Mike
In the US we run out of transponder codes almost weekly so we see proposed flight plans being assigned generic codes of 3100, 5400, etc. Since most approach controls have code subsets assigned to their facilities we can assign one of our local codes to any flight plan that has a generic code.
As for Mode S some facilities have the Mode S antennas and most don't.
Mike
The way it is intended to work (at least in Europe) is that the Mode S ground station extracts the Aircraft Id (Flight Id) directly via the Mode S datalink. This means that there is no need for a Mode A code/callsign look-up at the centre for Mode S equipped aircraft which will all have the same Mode A code. This frees up Mode A codes for non-Mode S targets.
Before this can happen we need operational Mode S radars, aircraft that support this feature, changes at the centre ….
I hope we can struggle on for a bit longer.
Before this can happen we need operational Mode S radars, aircraft that support this feature, changes at the centre ….
I hope we can struggle on for a bit longer.
Last edited by RaRadar; 27th Nov 2002 at 23:11.
Beady Eye
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Have taken some 'expert' advice on this now.
Mode 'S' will not appear anytime soon in UK. Although its essentially a software upgrade for the ATC radars the main UK radars require to be replaced (not only for mode 'S'). NATS had a 10 year plan to replace them all, but the cost is now £150million and with the HUGE debt NATS has the interest repayments have crippled that size of investment.
In UK during the summer usage of mode 'A' squawks reaches 95%.
Mode 'S' will not appear anytime soon in UK. Although its essentially a software upgrade for the ATC radars the main UK radars require to be replaced (not only for mode 'S'). NATS had a 10 year plan to replace them all, but the cost is now £150million and with the HUGE debt NATS has the interest repayments have crippled that size of investment.
In UK during the summer usage of mode 'A' squawks reaches 95%.
Thread Starter
Thanks for the info, all.
BDiONU
3) Is the proprotion of Mode A codes in use published somewhere?
4) You seem to be suggesting that the upgrades to ground equipment to take advantage of Mode S will be delayed against an original plan. Are there details published of a) the original plan and b) the revised schedule, or are you deducing the inevitability of delay from NATS's dire financial situation?
Mike
5) What is the FAA policy on aircraft equipage with Mode S? Is it required on aircraft over a certain size, or Part 121/135 or something else? What's the plan for the future?
6) What are the consequences of the code shortage? Does it delay flights? Do you limit capacity to cope with the extra workload of having to use these local codes? What's the "cost" of the problem?
BTW I can answer part of my question 1 from published Eurocontrol Mode S stuff. When Mode S is fully implemented, a conspicuity (non-unique) Mode A code will be allocated to aircraft. But I would appreciate any guidance as to how far down the road to Mode S we have to go before discrete Mode A codes start being preserved by that process.
BDiONU
3) Is the proprotion of Mode A codes in use published somewhere?
4) You seem to be suggesting that the upgrades to ground equipment to take advantage of Mode S will be delayed against an original plan. Are there details published of a) the original plan and b) the revised schedule, or are you deducing the inevitability of delay from NATS's dire financial situation?
Mike
5) What is the FAA policy on aircraft equipage with Mode S? Is it required on aircraft over a certain size, or Part 121/135 or something else? What's the plan for the future?
6) What are the consequences of the code shortage? Does it delay flights? Do you limit capacity to cope with the extra workload of having to use these local codes? What's the "cost" of the problem?
BTW I can answer part of my question 1 from published Eurocontrol Mode S stuff. When Mode S is fully implemented, a conspicuity (non-unique) Mode A code will be allocated to aircraft. But I would appreciate any guidance as to how far down the road to Mode S we have to go before discrete Mode A codes start being preserved by that process.
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bookworm
3) Not to the best of my knowledge. I would say its buried in one of NATS (in confidence) papers somewhere. I have access to several NAS experts and asked them.
4) The original plan was in the long term NATS strategic business plan and was due to be complete in 10 years time. This plan is now on hold. No deduction on my part. No, these details are not published in the public domain. If you're a NATS employee mail me and I will point you to the plan on the intranet, its not a secret.
Sorry if I seem to be only telling 'bits' but obviously company confidentiality forbids indiscretion.
Part answer to 6) for UK is that because NAS FLAT tracks aircraft the UK does have the ability to use specific codes for more than one aircraft. So it is quite possible to have several aircraft on the same (preferably one of the sector discreet codes) code, but with the TDB displaying the correct callsign etc. But we do not do that.
4) The original plan was in the long term NATS strategic business plan and was due to be complete in 10 years time. This plan is now on hold. No deduction on my part. No, these details are not published in the public domain. If you're a NATS employee mail me and I will point you to the plan on the intranet, its not a secret.
Sorry if I seem to be only telling 'bits' but obviously company confidentiality forbids indiscretion.
Part answer to 6) for UK is that because NAS FLAT tracks aircraft the UK does have the ability to use specific codes for more than one aircraft. So it is quite possible to have several aircraft on the same (preferably one of the sector discreet codes) code, but with the TDB displaying the correct callsign etc. But we do not do that.
Thread Starter
Sorry if I seem to be only telling 'bits' but obviously company confidentiality forbids indiscretion.
I'm trying to work out how to respond to the CAA's Regulatory Impact Assessment that would have aircraft operators spending hundreds of millions of pounds on Mode S related avionics. The cost benefit analysis, dating from 1998, hangs on overcoming two major issues, Mode A code shortages and RF congestion in the 1090 MHz region. The claimed benefit appears to be very sensitive to how close the current system is to saturation, and I'm trying to put together a picture of how accurate 1998 CBA will be.
Part answer to 6) for UK is that because NAS FLAT tracks aircraft the UK does have the ability to use specific codes for more than one aircraft. So it is quite possible to have several aircraft on the same (preferably one of the sector discreet codes) code, but with the TDB displaying the correct callsign etc. But we do not do that.
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bookworm
O I C. Before 9/11 traffic levels were rising year on year at about 6%, so saturation point would have been very much more quickly reached than at current traffic levels (although they are rising on internal flights with the boom in low cost carriers). I should think that the CBA in '98 was based on the pre 9/11 traffic levels and predictions.
RF congestion has been addressed to some extent by the introduction of 8.33 frequency spacing.
NAS is the UK's Flight Data Processing computer system and is absolutely integral to ATC in the UK. It processes the flight plans it gets from Brussels and distributes the flight data to all the relevant ATC sectors. It allocates the mode 3A code. It sends beacon estimates to units external to the NAS system and internally to NAS equipped units.
The reason it can send estimates is because it is linked into the UK radar system and tracks flights using their SSR code. NAS will 'watch' for an aircraft to get airborne and when it 'see's' the squawk it pairs it to the flight plan which NAS allocated the squawk to. It then tracks the flight and 'knows' its route, hence Flight plan Aided Tracking (FLAT). In addition to using radar NAS has a simple 'idea' of particular aircrafts speed, climb rate, rate of turn etc. plus it uses forecast upper winds to give estimates for beacons along the flights route. As an aside it is this 'idea' which we are very keen to have modernised to vastly improve our trajectory prediction (TP). More upper winds put into the airspace model, more realistic aircraft performances based on length of flight etc. The more accurately we can predict an aircraft's flight profile the more accurately we can predict where it'll be in the future and hence a big step forward to medium term conflict alert instead of our current short term version.
Not unusual for NAS to pair a track to a flight if, say the pilot has input the wrong squawk. Once the aircraft squawks the correct squawk its necessary to 'break' the pairing to allow NAS to correctly pair it up again. I have to admit I did not understand the technical reasons why it is possible to have more than one aircraft on the same squawk and still have the correct callsign etc. showing on the radar. Our 'professor' talks a much higher language than us mere mortals
but he assures me it is feasible.
However I think I may have lead you slightly up the garden path because I'm talking about UK and I suspect the real problem lies within the ORCAM region, but I don't know.
Sorry to burble on at length but couldn't think of a way to precis things. And if anyone can provide a better explanation of NAS than my rather off the cuff one please feel free to correct me
RF congestion has been addressed to some extent by the introduction of 8.33 frequency spacing.
NAS is the UK's Flight Data Processing computer system and is absolutely integral to ATC in the UK. It processes the flight plans it gets from Brussels and distributes the flight data to all the relevant ATC sectors. It allocates the mode 3A code. It sends beacon estimates to units external to the NAS system and internally to NAS equipped units.
The reason it can send estimates is because it is linked into the UK radar system and tracks flights using their SSR code. NAS will 'watch' for an aircraft to get airborne and when it 'see's' the squawk it pairs it to the flight plan which NAS allocated the squawk to. It then tracks the flight and 'knows' its route, hence Flight plan Aided Tracking (FLAT). In addition to using radar NAS has a simple 'idea' of particular aircrafts speed, climb rate, rate of turn etc. plus it uses forecast upper winds to give estimates for beacons along the flights route. As an aside it is this 'idea' which we are very keen to have modernised to vastly improve our trajectory prediction (TP). More upper winds put into the airspace model, more realistic aircraft performances based on length of flight etc. The more accurately we can predict an aircraft's flight profile the more accurately we can predict where it'll be in the future and hence a big step forward to medium term conflict alert instead of our current short term version.
Not unusual for NAS to pair a track to a flight if, say the pilot has input the wrong squawk. Once the aircraft squawks the correct squawk its necessary to 'break' the pairing to allow NAS to correctly pair it up again. I have to admit I did not understand the technical reasons why it is possible to have more than one aircraft on the same squawk and still have the correct callsign etc. showing on the radar. Our 'professor' talks a much higher language than us mere mortals
but he assures me it is feasible.However I think I may have lead you slightly up the garden path because I'm talking about UK and I suspect the real problem lies within the ORCAM region, but I don't know.
Sorry to burble on at length but couldn't think of a way to precis things. And if anyone can provide a better explanation of NAS than my rather off the cuff one please feel free to correct me
Thread Starter
Thanks for the detail BDiONU
Just as a point of clarification, the supposed benefit is relief of congestion of the radio spectrum around 1090 MHz where the transponders work, not of the aeronautical comms RT frequencies. I thought exactly as you did when I read the "RF congestion" section title in the CBA, but what they're getting at is basically that the selective nature of Mode S means that there's less going on at that frequency.
RF congestion has been addressed to some extent by the introduction of 8.33 frequency spacing.
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Hmm.... My old mate Take3 etc is more or less right, but i seem to recall that CCDS (Code/callsign distrubution system) allocates (and pairs) codes issued in the London FIR.
Hence when NAS is unavailable (shutdowns/ FLOPS) CCDS is still there so you can manually pair up code / callsign / dest / exit point.
I think?
Rgds BEX
Hence when NAS is unavailable (shutdowns/ FLOPS) CCDS is still there so you can manually pair up code / callsign / dest / exit point.
I think?
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This is all v interesting, even if it has wandered slightly off track. Now I've got a question for the techy types:
The consoles in the MASOR use the CCDS for code/callsign pairing, but there is also something that provides beacon estimates as well. Is it the same system (NAS) as used by the civil sectors, or is there a seperate system that provides estimates in the MASOR?
TIA
Hippy.
The consoles in the MASOR use the CCDS for code/callsign pairing, but there is also something that provides beacon estimates as well. Is it the same system (NAS) as used by the civil sectors, or is there a seperate system that provides estimates in the MASOR?
TIA
Hippy.
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Aha..... There you go. Yes that would make sense wouldn't it? I knew CCDS came into it Somewhere.
I have a dim and distant memory of code allocation pads in use on the assistant positions at ScATTC, and lots of phone calls down south with each estimate.
Even more "slight" thread creep (sorry). Just when will NAS be replaced? The Americans are in the process right now. How far have "we" got?
Anyone know for real?
Rgds BEX
I have a dim and distant memory of code allocation pads in use on the assistant positions at ScATTC, and lots of phone calls down south with each estimate.
Even more "slight" thread creep (sorry). Just when will NAS be replaced? The Americans are in the process right now. How far have "we" got?
Anyone know for real?
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I confess to being a little lost in the large amount of detail in the replies to Bookworms question.
From the light aviation standpoint, where most airplanes do not have an FMS, so cannot give the added information, and are probably only on flight planned routes for a small percentage of their flying, the main advantage of equipping light airplanes with Mode S appears to be in avoiding TCAS uncertanties.
Bookworm, when you have absorbed all the information, could you post your conclusions as you seem to have a greater understanding of the salient points than do I. Thanks.
From the light aviation standpoint, where most airplanes do not have an FMS, so cannot give the added information, and are probably only on flight planned routes for a small percentage of their flying, the main advantage of equipping light airplanes with Mode S appears to be in avoiding TCAS uncertanties.
Bookworm, when you have absorbed all the information, could you post your conclusions as you seem to have a greater understanding of the salient points than do I. Thanks.
Thread Starter
Happy to do that bluskis.
I'm actually thinking of the cost-benefit issues for a Mode S Elementary setup - in other words you pull out your Mode A/C transponder and stick in a Mode S one, connected to nothing more than an encoding altimeter. No FMS required. That's what's proposed for aircraft < 5700 kg in the TMA for 2005.
The purported advantages of this rest on two issues, both related to capacity.
1) There are a limited number of Mode A codes available
2) There's congestion at SSR RF frequencies when Mode A/C is used.
I'd like to understand whether these are real issues, now, and if not, when are they likely to be serious limits to capacity.
I'm actually thinking of the cost-benefit issues for a Mode S Elementary setup - in other words you pull out your Mode A/C transponder and stick in a Mode S one, connected to nothing more than an encoding altimeter. No FMS required. That's what's proposed for aircraft < 5700 kg in the TMA for 2005.
The purported advantages of this rest on two issues, both related to capacity.
1) There are a limited number of Mode A codes available
2) There's congestion at SSR RF frequencies when Mode A/C is used.
I'd like to understand whether these are real issues, now, and if not, when are they likely to be serious limits to capacity.
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For the computery and mathematically uncallenged the current mode A code numbers are octal - 0 to 7. You will never see an 8 in an ssr code. Digital, even 4 digits, can go to 9999, lots more but not enough. Individual 'ident' is the answer but a few years away yet I fear.